This atypical tomato developed a dark discoloration just under the skin of the ripe fruit. When cut open, seeds within the tomato fruit were germinating. This physiological disorder is known as vivipary, where the seeds germinate while still in the fruit. It is suspected to be caused by plant stress such as drought, water stress, or potassium deficiency within the fruit. The fruit are still edible.
Photo Source: Mike Bush, Washington State University Extension, Yakima, WA